In order to meet the demands of compact, light-weight and conveniently portable electronic products, research and development of electronic product manufacturers are directed to and focused on miniaturization of electronic components.
Printed circuit boards are one of the essential components of many electronic products, such as smart phones, and served to provide electronic signal transmission among different electronic components. Several technical solutions have been proposed, such as high density interconnection (HDI), by printed circuit board manufacturers to reduce the size or thickness of printed circuit boards, so as to form denser trace connections within the same or even smaller size or thickness.
For example, the HDI technique employs several means to achieve high trace density, including laser blind hole drilling, small trace width and high performance thin type materials. The increase of density greatly improves the connections per unit area. In addition, the more advanced “any layer” HDI multi-layer printed circuit boards use micro-blind hole structures through plated hole filling and stacking to further achieve more sophisticated interlayer connections.
Generally, “any layer” HDI technique is different from the manufacturing processes of conventional printed circuit boards and primarily uses build-up methods to form the trace layers and insulation layers. Each build-up cycle involves lamination of prepregs and copper foils, laser drilling, hole metallization, and trace formation, including exposure, lithography, etching, etc. The aforesaid steps are carried out according to the number of layers, such as eight to fourteen layers for an ordinary mobile phone circuit board, needed to be formed to complete the multi-layer printed circuit boards.
Due to the high precision requirements of the HDI technique, positional change of interlayer electrical connections of buried holes and blind holes needs to be controlled during the process. If the lamination process causes severe deformation, the final products won't be able to meet the requirements and have to be discarded, which will increase the production costs.
Accordingly, there is a need to provide multi-layer printed circuit boards with high dimensional stability and excellent signal transmission property.